Small portable electrolytic sodium hypochlorite on site generators

ABSTRACT

The present invention describes four preferred embodiments of an apparatus aimed to the production of a dilute solution of sodium hypochlorite. It uses the process of the electrolysis of a dilute solution of sodium chloride in water by means of two metallic electrodes immersed in the solution. The electricity needed may be delivered by a range of sources like disposable cells (alkaline), rechargeable batteries, photovoltaic modules (PVM) or electromechanical generators, like alternators or dynamos, moved by human power. All the apparatus described operate in batch mode. They are small lightweight portable units, easily transportable anywhere, in remote areas or emergency situations where chemicals or electricity is not available. Main use is the purification of drinking water, but also the production of sterilizing solutions for wound disinfection, washing etc.

BACKGROUND OF THE INVENTION

A number of electrochemically generated oxidants may be used to purifywater: for instance Hydrogen Peroxide and ozone, which are difficult andcritical to produce with simple devices to be operated on site and inthe field. Therefore the most traditional oxidizing agent in thesecircumstances is Sodium Hypochlorite solutions or chlorine in the formof solid compounds. It should be noted that this compounds are quitecritical to storage and deliver, particularly in hot and remote areas.The alternative solution is to produce Sodium Hypochlorite on site. Itcan be easily obtained by simple electrolysis of a dilute solution ofSodium Chloride in water.

The electrolysis process is well known. It is carried out by preparing asolution of Sodium Chloride in water, of proper concentration, and placeit into an electrolysis cell composed of a container equipped with twoelectrodes, one anode and one cathode, through which is passed a dcelectric current.

The electrodes are made of a chemically inert metal, like Titaniumcoated with oxides of noble metals like Ruthenium, Titanium, Lanthanum,Iridium, etc. They have semiconductor properties and are excellentcatalysts for chlorine generation. This electrodes are named DSA(dimensionally stable anodes) and the coatings are proprietary.

In a cell of this type the anode and cathode are placed in the cellcavity without diaphragm or membranes separating them. In this way theelectrochemical reaction products, Chlorine at the anode and SodiumHydroxide at the cathode, react producing Sodium Hypochlorite.

The current density on the electrodes can vary from 0.05 to 0.5 Amp/cm².

The current efficiency depends on temperature. (a high temperatureshould be avoided as it promotes the formation of undesired ChloratesClO₃), from pH of the solution. The energy conversion efficiency dependson the concentration of the saline solution, on the gap between theelectrodes, and from the geometry of the cell: all this parametersinfluence the conductivity of the solution and consequently the ohmiclosses of the cell itself.

SUMMARY OF THE INVENTION

The present invention is related to the production of SodiumHypochlorite by means of electrolysis of a solution of Sodium Chloridein water.

This device has been conceived to fulfill the following specifications:

a) produce Sodium Hypochlorite in batch mode, delivering always the samequantity of equivalent chlorine. In other words the hypochlorite amountproduced must be reproducible irrespective from the saline solutionconcentration or cell voltage,b) have a current efficiency from 80 to 90%,c) have an energy conversion efficiency as high as possible (in terms ofWh/g of equivalent Chlorine produced), of the order of 2.5 to 3.5 Wh/g.d) operate in a sure and reliable way for a wide range of concentrationsof the saline solution, from 1 to 5% by weight,e) operate with renewable sources of energy,f) be portable and lightweightg) be low-cost.h) be maintenance free,i) last for many years (5-10)

Points b), c), and e) allow the use of this device powered by: solar PVmodules, rechargeable batteries or manually operated electromechanicalgenerators. All this can be obtained by means of a small electrolyticcell equipped with titanium DSA electrodes, powered by a power supplycircuit that delivers a specified quantity of electricity (Amp*sec),this circuit being powered by a source of electromotive force (emf), inorder to produce a specified quantity of sodium hypochlorite. For thisreason this device is very useful when employed in isolated or remotesites, where electricity or chemicals are not available.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the first preferred embodiment.

FIG. 2 illustrates the block diagram of the power supply referred to thefirst preferred embodiment.

FIG. 3 illustrates the second preferred embodiment.

FIG. 4 illustrates the block diagram of the power supply referred to thesecond preferred embodiment

FIG. 5 illustrates the third preferred embodiment.

FIG. 6 illustrates the block diagram of the power supply referred to thethird preferred embodiment.

FIG. 7 illustrates the fourth preferred embodiment.

FIG. 8 illustrates the block diagram of the power supply referred to thefourth preferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The apparatus is made essentially of three parts:

1—An electrolytic cell made of a plastic transparent cylindrical vesselthat has means to measure a specific quantity of water. The vessel isprovided with a lid provided with a small cavity which is used tomeasure the quantity of salt to be introduced into the cell.

The cell capacity ranges from 10 to 50 ml, depending on the quantity ofthe Sodium Hypochlorite to be produced. The amount of salt measured withthe cavity on the lid is such as to form, together with the quantity ofwater measured in the cell, a solution of specified concentration, whichcan vary from 1 to 5% by weight. The cell is equipped with two or moretitanium DSA electrodes, whose dimensions are related to the appliedcurrent and to the amount of Sodium Hypochlorite that has to beproduced.

2—An electronic power supply management circuit.3—An electromotive force (emf) source that could be of many types:disposable cells, rechargeable batteries, supercapacitors, solarphotovoltaic modules, and electromechanical generators (alternators ordynamos) moved by hand or pedal power.

The power supply management circuits related to the four embodimentsillustrated in FIGS. 1, 3, 5 and 7 will be illustrated in FIGS. 2, 4, 6and 8 and described below.

FIG. 1 shows one example of the first embodiment. It is a small portableunit operating in batch mode. It is composed of a cylindricaltransparent container 1, open at one end, with a capacity of 10-15 mL,preferably of 10 mL. Inside are fitted two electrodes, one anode 2 inthe form of a rectangular strip of titanium (DSA), and one cathode 3also in the form of a rectangular strip facing the anode. The cathodecan be of DSA titanium or stainless steel.

A circular line 10 is engraved on the inside wall of the cell toindicate the water level. The cell is closed with the lid 4 in which acavity 5 is used to measure the quantity of salt necessary to preparethe solution. In the compartment 6 is placed the electronic power supplyas described below. The diaphragm 7 separates the power supplycompartment 6 from the battery compartment 8. In this example the unitis equipped with a couple of 1,5 Volts alkaline D cells (disposable).From manufactured prototypes the operating characteristics were thefollowing: a saline concentration raging from 1.5 to 2.5% by weight, acell current ranging from 300 to 500 mA, and the quantity of electricitydelivered to the cell ranging from 4.5 to 7.5 Amp×sec. Under theseconditions the cycle duration was about 15 seconds and the equivalentChlorine produced ranged from 1.2 to 2.2 mg. The dimensions of the unitare approx. 250 mm length and 50 mm diameter.

It is obvious that the same embodiment can be made using rechargeablebatteries (NiMH or NiCd). In this case the power management circuit willbe provided with a battery charging circuit powered by an externalextension to be plugged to the electricity grid. Another embodimentcomprised in the one described above could be one with larger batteriesand consequently larger electrolytic cell. All this in order to producelarger amounts of sodium hypochlorite.

The electronic power supply block diagram relative to the firstembodiment (FIG. 1) is illustrated in FIG. 2. It must be remembered thatthis kind of cell operates in batch mode and therefore for a limitedperiod of time after being turned on. The emf source 1 (for this casedisposable cells or rechargeable batteries) is connected to a latchcircuit 7 (mechanical or solid state relay) operated by a push buttonswitch 8. When the switch 8 is pressed a dc-dc switching inverterstabilizer 2 (that can be a buck or boost or buck-boost orconstant-current type) is connected to the source 1, which delivers a dcvoltage to the electrolytic cell 3. The current that passes through thecell is time-integrated by the integrator circuit 4. During the time thecell is in operation and when the value of the time integral of thecurrent (i.e. the value of the product Amp×sec, from circuit 4) hasreached a preset value, a comparator 5 (whose threshold sets the Amp×secvalue) opens the latch 7, turning off the current to the electrolyticcell and concluding the time cycle. The dc-dc inverter is necessary tostabilize the supply current to the electrolytic cell against the typeand stability of the source 1. A second comparator 6 has the role ofopening the latch circuit 7 in case it is accidentally activated withthe cell empty. The power supply circuit just described, which is basedon the condition Current×time=constant, affords one to obtain always thesame amount of Chlorine (Sodium Hypochlorite) independently from thevalue of the voltage delivered from the source 1 or the saline solutionconcentration (which influences the conductivity of the solution). Onthis regard it should be noted that the electrolytic cell operates atconstant current.

FIG. 3 shows a second example. It is also a small portable unitmeasuring only 21 cm length and 6.5 cm diameter. It also operates inbatch mode. The characteristic of this unit is that the energy issupplied by a hand-crank driven alternator. From FIG. 3 the cylindricalcell 1 is fitted with two electrodes of DSA titanium 2. On the cellinner wall a line 10 is engraved to indicate the water level. The cellis closed with the cap 3 in which a cavity 4 is used to measure theamount of salt necessary to prepare the solution. The capacity of thecell can be in the range of 15-25 mL, preferably of 20 mL. The tworectangular electrodes are spaced 3 mm, placed in the center of the celland measure preferably 30×10 mm. The external faces of the electrodesare insulated in order to optimize the conversion efficiency. Thealternator 5 is driven by gears 6 and the handle 7. The entire body 8contains also the electronic hardware 9. In this example a 3 Wattalternator was employed delivering 6 Volts at 500 mA. By winding forabout 1 minute an amount of equivalent chlorine of 3.5 mg could beproduced. The power supply for this example can be of two types:

The first is illustrated in FIG. 4, where 1 is the alternator (ordynamo) directly connected to the storage 2 that could be asupercapacitor or a rechargeable battery. The storage is connected to athreshold circuit 3 that senses the charge level of the storage. Whenthis level is equal to a preset value the circuit 3 triggers the latchcircuit 4 that connects the storage to the electrolytic cell 5. Thecurrent that passes through the cell is time-integrated by theintegrator circuit 6. During the time the cell is in operation and whenthe value of the time integral of the current (i.e. the value of theproduct Amp×sec, from circuit 4) has reached a preset value, acomparator 7 (whose threshold sets the Amp×sec value) opens the latch 4,turning off the current to the electrolytic cell and concluding the timecycle.

The second is of the same type as the one for the following embodiment(FIG. 5), illustrated in FIG. 6, and described later.

A third embodiment is illustrated in FIG. 5. This unit, operating alsoon batch mode, is similar to previous unit. The electric energy is alsoprovided by a hand driven generator (alternator) but of higher power. Inthis example the alternator is directly connected to a dc-dc constantcurrent converter without an intermediate storage. When the generator isoperated a timer turns on automatically which switches off the currentto the electrolytic cell after a preset time (one minute for thisexample). In this way the condition Amp*sec=constant is fulfilled. Thepower supply for this unit is the same as for the second optiondescribed for the previous example and illustrated in FIG. 6. Theelectrolytic cell 1 is placed at one end of the unit and has a capacityof 75 mL. The electrode set 2 is composed of three electrodes of DSAtitanium. The central electrode is the anode while the two lateralelectrodes are the cathode. The electrodes area may vary from 10 to 20sqcm, preferably 15 sqcm. On top of the cell the revolving cap 3 has ahole. The diameter and length of the hole determine the amount of saltthat can be dosed for the saline solution. This revolving cap is fittedin a cavity on top of the cell. The cavity has a hole of the samediameter of the hole on the revolving cap. By turning the cap the twoholes will coincide permitting the salt to fall into the cell. The otherparts of this unit are: the housing 4, the crank 5, the alternator 6,the gear box 7, the power supply 8, placed under the handle 10, and thewarning light 9.

With a saline concentration of 1.65%, and a current of 2 Amp lasting oneminute a quantity of equivalent chlorine of 40 mg has been obtained, atan efficiency near to 90%. The dimensions of this example are 26×16×12cm.

The power supply employed for the above described embodiment, as alreadyanticipated is illustrated in FIG. 6. It differs from the previous (FIG.4) as it operates without the energy storage. Block 1 is the mechanicalgenerator (alternator) which is connected to a constant currentregulator 2, directly connected to the electrolytic cell 4 through thethreshold circuit 3. The threshold circuit senses the current deliveredto the electrolytic cell. When this current reaches a preset value, i.e.the correct value to operate the electrolytic cell, a pulse generator 5is activated that, in combination with the counter 6, constitute atimer, which is set to a specific preset count. When the counter stops ashut-off pulse 7 is sent to the regulator 2 shutting off the current tothe electrolytic cell. It should also be noted that if the alternator isstopped before the preset time has elapsed also the counter stopswithout loosing the already counted pulses. When the alternator is againoperated the counter continues counting. In fact block 7 is a smallcapacitor storage with the purpose of keeping the counter 6 alive for afew minutes even if the alternator is momentarily stopped before endingthe preset counts.

A fourth example is shown in FIG. 7. Also this unit operates in batchmode. The electricity source is a small photo-voltaic module 1 of 0.5Watt. The lid 2 has the double purpose to protect the PV module whenclosed or act as a mirror to increase the solar radiation on the PVmodule when it is exposed to the sun. This is illustrated in FIG. 7 a.The electronic hardware, power supply and storage, are in thecompartment 3. The electrolytic cell, 4, is fitted with a revolving cap5 similar to the one described above for the third example. Its capacityis approximately 20 mL. The electrodes 6 are a pair of titanium strips,coated as already described, spaced from 2 to 4 mm, preferably 3 mm, andhaving a surface area from 4 to 5 sqcm, preferably 3.5 sqcm. With a saltsolution composed of 600 mg of salt in 20 mL of water, a cell current of250 mA lasting 1.5 minutes the equivalent chlorine produced was 6 mg.This was achieved with a full sun exposure of a few minutes. Thedimensions of this unit are approximately 18×14×5 cm. The power supplycircuit for this embodiment is similar to the one described in FIG. 2.

With reference to FIG. 8 the power supply circuit is composed by aphotovoltaic module (PVM) 1 connected to a voltage regulator 3. Diode 2has the purpose to isolate the PVM from the rest of the circuit. Theregulator 3 delivers a voltage for charging the storage capacitance 4.It should be noted that that the PVM voltage must be higher than themaximum permitted voltage for the storage capacitance. A thresholdcircuit 5 senses the voltage of the storage capacitance. It turns on awarning light when the capacitance voltage is at its maximum. This meansthat the storage voltage can be used to run the electrolytic cell. Torun the electrolytic cell the circuit 6 must be activated. This circuitis a switch (solid state) with latch. By pressing the button-switch 7the switch 6 closes connecting the storage capacitance 4 to theelectrolytic cell 8. An integrator circuit 9 senses the current thatflows through the electrolytic cell and integrates it with a specifiedtime constant. In practice the circuit 9 measures the current-timeproduct (mA×sec) which expresses the quantity of electricity deliveredto the electrolytic cell and consequently the quantity of hypochloriteproduced. The circuit 9 is set to a predetermined quantity of mA×sec,which when reached, triggers, by means of the comparator 10, an impulseto the switch 6 which opens turning off the electrolytic cell. Thefunction of the integrator-comparator circuit is to deliver always thesame amount of electricity to the electrolytic cell 8 and consequentlyto produce the same amount of chlorine, irrespective from the salt(sodium chloride) concentration in the saline solution, and/or thecharge level of the storage 4.

1. Portable apparatus for the production of Sodium Hypochlorite by meansof the electrolysis of a dilute solution of Sodium Chloride in water,comprising a container in which is enclosed an electrolytic cell whichis composed by a vessel equipped with at least two electrodes made ofmetal like titanium or titanium coated with noble metals like ruthenium,tantalum, lanthanum oxides, suited to contain a predetermined quantityof diluted sodium chloride solution, an autonomous source of electricenergy and a circuit for connecting said source of electric energy tothe electrodes of the aforesaid electrolytic cell.
 2. Portable apparatusas claimed in claim 1 wherein said connecting circuit comprises meansfor interrupting the operation of said electrolytic cell after a timedelay in relation to the current intensity and time supplied to theelectrodes of said electrolytic cell, and to the concentration of thesolution introduced into said electrolytic cell.
 3. Portable apparatusas claimed in claim 1 and 2 wherein said connecting circuit comprisesmeans for stabilizing the current and/or the voltage delivered by saidautonomous source of electric energy to said electrodes of theelectrolytic cell.
 4. Portable apparatus as claimed in any one of thepreceding claims wherein said means for interrupting the operation ofthe electrolytic cell comprises an integrator circuit of the currentdelivered, in relation to time, to said electrodes of the electrolyticcell, the output of said integrator being connected to a comparatorcircuit that compares the value of the current integral provided by saidintegrator circuit with a predetermined reference value, said comparatorbeing connected to a switch in order to interrupt the current suppliedto the electrolytic cell when said current integral has reached apredetermined value.
 5. Portable apparatus as claimed in any one of thepreceding claims comprising a circuit which interrupts the electricenergy supply to said electrolytic cell in case of absence of SodiumChloride solution in said electrolytic cell.
 6. Portable apparatus asclaimed in any one of the preceding claims wherein said circuitcomprises a comparator circuit whose input is connected to theelectrodes of said electrolytic cell, and whose output is connected tosaid switch.
 7. Portable apparatus as claimed in any one of thepreceding claims wherein said switch consists of a mechanical relay. 8.Portable apparatus as claimed in any one of the preceding claims whereinsaid switch consists of a solid state relay.
 9. Portable apparatus asclaimed in any one of the preceding claims wherein said electricalenergy in the form of voltage or current delivered by the emf source isdetected by a threshold circuit of the Schmitt trigger type. 10.Portable apparatus as claimed in any one of the preceding claims whereinsaid means for voltage stabilization includes a dc (direct current)voltage stabilizer.
 11. Portable apparatus as claimed in any one of thepreceding claims wherein said means for current stabilization includes adc constant current stabilizer.
 12. Portable apparatus as claimed in anyone of the preceding claims wherein said means for voltage stabilizationincludes a converter from ac (alternate current) current to dc current.13. Portable apparatus as claimed in any one of the preceding claimswherein said power supply circuit includes a pushbutton switch to turnon said portable apparatus, said pushbutton switch being connected inseries with aforesaid switch.
 14. Portable apparatus as claimed in anyone of the preceding claims wherein said threshold circuit when itsenses a preset value of the constant current delivered to saidelectrodes of the electrolytic cell, a pulse generator is activated andconnected to a counter which is set to a specific preset count. When thecounter stops a shut-off pulse is sent to the said constant currentstabilizer shutting off the current to said electrodes of saidelectrolytic cell.
 15. Portable apparatus as claimed in any one of thepreceding claims wherein said pulse generator is connected between saidconstant current stabilizer and said counter.
 16. Portable apparatus asclaimed in any one of the preceding claims wherein said counter is setto a number of counts which determine the quantity of electric energydelivered to the electrodes of said electrolytic cell.
 17. Portableapparatus as claimed in any one of the preceding claims wherein saidelectrolytic cell comprises a vessel suited to contain a predeterminedquantity of Sodium Chloride diluted solution, said vessel being fittedwith said electrodes and being closed with a removable cover. 18.Portable apparatus as claimed in any one of the preceding claims whereinsaid vessel is made of transparent material bearing a reference notch toindicate the level of the solution when poured into said electrolyticcell.
 19. Portable apparatus as claimed in any one of the precedingclaims wherein said cover has a cavity suitable for dosage of the SodiumChloride to be introduced into said electrolytic cell in order toprepare the diluted Sodium Chloride solution.
 20. Portable apparatus asclaimed in any one of the preceding claims wherein said cover has acylindrical form with an eccentric hole. Said cover is free to rotate ina cylindrical housing having on its bottom a hole of the same diameterof the hole in said rotating cover, the two holes being coincident for aspecific position of said rotating cover.
 21. Portable apparatus asclaimed in any one of the preceding claims wherein said electrodes ofthe electrolytic cell have a rectangular shape, having a surface areacomprised between 1 and 15 square centimeters and being placed parallelto each other with a gap comprised between 1 and 5 mm.
 22. Portableapparatus as claimed in any one of the preceding claims wherein saidanode and said cathode are made of Titanium coated with noble metaloxides like ruthenium, tantalum, titanium, lanthanum, etc., said coatingbeing proprietary.
 23. Portable apparatus as claimed in any one of thepreceding claims wherein said connecting circuit is fitted into a sealedcompartment (hereinafter called first compartment) separated from saidelectrolytic cell and from another compartment (hereinafter calledsecond compartment) containing said autonomous electric energy source.24. Portable apparatus as claimed in any one of the preceding claimswherein said part of said container, called first compartment, ispermanently connected to the part of said container, called secondcompartment, being provided means for an electrical connection betweensaid connecting circuit, fitted in the first compartment, and saidelectric energy source fitted in said second compartment.
 25. Portableapparatus as claimed in any one of the preceding claims wherein saidconnecting circuit is provided with a cable for the connection to anexternal source of electric energy.
 26. Portable apparatus as claimed inany one of the preceding claims wherein said autonomous electric energysource comprises at least one electric cell (disposable type). 27.Portable apparatus as claimed in any one of the preceding claims whereinsaid autonomous electric energy source comprises at least onerechargeable battery.
 28. Portable apparatus as claimed in any one ofthe preceding claims wherein said autonomous electric energy sourcecomprises at least one supercapacitor.
 29. Portable apparatus as claimedin any one of the preceding claims wherein said autonomous electricenergy source comprises an alternator or dynamo.
 30. Portable apparatusas claimed in any one of the preceding claims comprising means for handdriving of said alternator or dynamo.
 31. Portable apparatus as claimedin any one of the preceding claims wherein said autonomous electricenergy source comprises a photovoltaic module (PVM).
 32. Portableapparatus for the production of Sodium Hypochlorite by means of theelectrolysis of a diluted solution of Sodium Chloride comprising any oneof the characteristics as herein described with reference to and asshown in the accompanying drawings.